1. Field
The present disclosure relates to a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery including the positive electrode.
2. Description of the Related Art
Lithium ion secondary batteries have high charging/discharging capacity, high driving potential, and good charging/discharging cycle characteristics, and thus demand has risen for using the lithium ion secondary batteries in motorcycles, electric vehicles, or hybrid electric vehicles, which use a portable information terminal, a portable electronic device, a small-sized electric energy storage device for home use, and a motor as driving sources. The lithium ion secondary batteries use, as an electrolyte, a non-aqueous electrolyte solution prepared by dissolving a lithium salt in an organic solvent, but there are safety concerns due to easy ignition and leakage of non-aqueous electrolyte solution. Thus, to improve safety of lithium ion secondary batteries, research has been actively conducted into an all solid-state lithium ion secondary battery using a solid electrolyte consisting of a non-combustible inorganic material (hereinafter, referred to as ‘all solid-state secondary battery’).
A nitride or an oxide may be used as the solid electrolyte of the all solid-state secondary battery, and due to its conductivity of lithium ions, a sulfide-containing solid electrolyte is considered as a promising material. However, when a sulfide-containing solid electrolyte is used, a reaction between a positive active material particle and a solid electrolyte particle may occur at an interface therebetween during charging of a battery, and thus an interfacial resistant component may be produced, resulting in an increase in resistance at the interface between the positive active material particle and the solid electrolyte particle (hereinafter, also referred to as ‘interface resistance’) during the movement of the lithium ions. Due to the increase in the interface resistance, the conductivity of lithium ions decreases, and thus output of the lithium ion secondary battery may be deteriorated.
In this regard, attempts have been made to reduce the interface resistance by coating a surface of a positive active material particle, e.g., LiCoO2 (hereinafter, also referred to as ‘LCO’), with another material.
However, a process of coating the surface of the positive active material particle with an oxide, e.g., SiO2, or a process of arranging a buffer layer or an interlayer between a positive electrode layer and a solid electrolyte layer is not sufficient enough to inhibit a reaction at the interface between the positive electrode active material particle and the solid electrolyte particle. Such a process rather requires further reduction in the resistance component.